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Applied Stochastic Hydrogeology$
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Yoram Rubin

Print publication date: 2003

Print ISBN-13: 9780195138047

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195138047.001.0001

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Vadose Zone, Part II : Transport

Vadose Zone, Part II : Transport

12 (p.312) Vadose Zone, Part II : Transport
Applied Stochastic Hydrogeology

Yoram Rubin

Oxford University Press

This chapter is an extension of our discussion on transport in chapters 7 to 10. Our goal here is to explore a few aspects of the transport problem which are unique to variably saturated soils. The heterogeneity of soils affects transport of solutes in the vadose zone in different ways. It leads to irregular and hard-to-predict spreading of the solutes. The solutes may be channeled through highly conductive flow channels where diffusion plays only a minor role. This may lead to concentrations which are high and travel times which are fast compared to what one may anticipate by assuming that the medium is homogeneous. Evidence for such behavior was found in field experiments (cf. Wierenga et al., 1991; Ellsworth et al., 1991; Ritsema et al., 1998; Sassner et al., 1994) and in large-scale laboratory experiments (Dagan et al., 1991). Hence, the effects of heterogeneity must be recognized and modeled. The effects of heterogeneity can be modeled by employing the stochastic concepts discussed in earlier chapters. The approach for modeling contaminant transport which is the least restrictive in terms of assumptions introduced is the MC simulation. This approach will be reviewed briefly in section 12.1. Modeling of the mean concentration along our discussion in chapter 8 is computationally less demanding compared to MC simulations, yet is less informative since the concentration in the field can hardly be expected to be equal to its expected value. Applications along that line are limited since deriving the macrodispersion coefficients needed for such an undertaking is difficult. Nonetheless, we shall discussed this approach in section 12.2, for the insight into the transport processes it provides. A few simple models are available for gravitational flow through shallow depths. These methods are of course limited in applications, yet they are less demanding in terms of data requirements and the computational efforts involved. Such methods are the focus of the last section in this chapter. The concept of MC simulation was discussed in earlier chapters.

Keywords:   Bresler-Dagan (BD) Model, Infiltration, Scaling, Unit gradient

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